The invention makes use of vacuum rolls for transferring the web from one position to another--vacuum rolls in folding having been long used--see co-owned U.S. Pat. No. 2,165,786. Further, the concept of having two webs with the transverse lines of perforation offset, so as to develop an interfolded product, is also well known, see U.S. Pat. No. 3,044,766. More recently, it has been desired to operate at higher speeds and the removal of the interfolded stacked product has constituted a speed limitation. This is particularly true with "short counts", viz., relatively small stacks. Therefore, it was desirable to provide alternate interfolders so that when the stack was being removed from one interfolder, the other could be developing a subsequent stack. Representative of this is U.S. Pat. No. 4,494,741.
A number of disadvantages characterized the '741 Patent construction. There, two webs were combined immediately after perforation and then had to be separated at transition from one interfolding position to the other. Further, the '741 Patent required a precise balance between perforation bond strength, web porosity and the vacuum source. Too much vacuum effect and the outer of the superposed webs did not stay on its roll, whereas too little would not result in a breaking of the bonds.
According to the instant invention, the combination of the two webs is delayed until the last operation before interfolding. By this means, the transition from one interfolding position to the other requires only redirecting the paths of the two webs as individual webs. An advantageous aspect of the invention is the provision of two pluralities of vacuum rolls defining four equal length paths between cut-off devices and interfolders. To effectuate the switch from one interfolding position to another, I employ vacuum rolls that are selectively vacuumized, depending upon the path to be chosen.